Exemplary embodiments of the present invention relate to an orthomode coupler for an antenna system, particularly for a multi-feed antenna. The orthomode coupler comprises a first signal waveguide for a first RF signal that can propagate in the first signal waveguide, along a first axis. It comprises a second signal waveguide for a second RF signal that can propagate in the second signal waveguide, along a second axis, where the second axis is disposed parallel to the first axis. The first and the second signal waveguide end in a septum polarizer. A transmission and reception signal can propagate along a third axis of a common signal waveguide of the orthomode coupler, where the third axis runs parallel to the first and the second axis, where the common signal waveguide is coupled with the septum polarizer.
Orthomode couplers separate or combine two orthogonal, linearly polarized waves. In this connection, the first and the second signal waveguide, which are also referred to as feed waveguides, usually stand perpendicular on one another. The orthogonal placement of the feed waveguides, which are usually configured as rectangular waveguides, is due to the assignment to polarizations that are orthogonal to one another, at the common gate (the common signal waveguide).
If the orthomode coupler is used in a multi-feed antenna system, great packing density of the orthomode coupler is required, thereby making parallel placement of its feed waveguide advantageous or actually compulsory. When the feed waveguides are conducted in parallel, however, it is difficult to ensure polarization purity over the greatest possible bandwidth.
An orthomode coupler is known from P. Sarasa, M. Diaz-Martin, J.-C. Angevain, C. Mangenot: “New Compact OMT Based on a Septum Solution for Telecom Applications,” 32nd ESA Antenna Workshop, 2010, which coupler has rectangular feed waveguides disposed in parallel. Because of the parallel placement of the feed waveguides, this orthomode coupler can easily be integrated into multi-feed antenna systems. A disadvantage of the orthomode coupler described in the publication is its small bandwidth. Furthermore, its polarization is tilted by 45° relative to the field intensity vectors in the signal waveguides. This tilting by 45° makes direct connection of a distributor network more difficult, and makes the use of so-called twists necessary, if applicable.
Accordingly, exemplary embodiments of the present invention provide an orthomode coupler in which a great bandwidth and great polarization purity can be achieved, in comparison with the variants known from the state of the art.
The invention provides an orthomode coupler for an antenna system, particularly for a multi-feed antenna. The orthomode coupler comprises: a first signal waveguide for a first RF signal that can propagate in the first signal waveguide, along a first axis; a second signal waveguide for a second RF signal that can propagate in the second signal waveguide, along a second axis, where the second axis is disposed parallel to the first axis; a septum polarizer in which the first and second signal waveguide end; and a common signal waveguide having a third axis, along which a transmission and reception signal can propagate, where the third axis runs parallel to the first and the second axis, and where the common signal waveguide is coupled with the septum polarizer. According to the invention, the common signal waveguide comprises a further polarizer.
The orthomode coupler according to the invention therefore combines a septum polarizer with a further polarizer. In the transmission case, a circularly polarized wave is first generated by the septum polarizer. This wave is converted to a linearly polarized wave by the polarizer. In the reception case, the polarizer generates a circularly polarized wave from a linearly polarized wave. The septum polarizer generates a linearly polarized wave from the circularly polarized wave. In this way, it is possible to adjust the direction of the polarization vector in any desired manner. Furthermore, a high level of cross-polarization suppression is achieved over a great bandwidth by means of the combination. Likewise, the orthomode coupler according to the invention makes a high level of polarization purity available.
In particular, it is provided that the first RF signal in the first signal waveguide and the second RF signal in the second signal waveguide are polarized orthogonal to one another. In other words, this means that polarizations that are orthogonal to one another are assigned to the inputs of the septum polarizer.
The further polarizer can optionally be configured as a groove polarizer, as a crosspiece polarizer, or as a post polarizer. The cross-section of the further polarizer can optionally be configured to be round or rectangular.
In particular, it is practical if the septum polarizer and the further polarizer are connected with one another by way of a coupling element. It is particularly preferred, in this connection, if the coupling element has a round cross-section, so that the septum polarizer and the further polarizer can be rotated relative to one another about its central axis. The direction of the polarization vector can be adjusted as desired, in simple manner, by means of a rotation of the further polarizer about its central axis.
The orthomode coupler according to the invention is configured, by means of the combination of the septum polarizer with a further polarizer, in such a manner that the frequency response of the septum polarizer is partially compensated by the frequency response of the further polarizer. The bandwidth and the polarization purity are significantly improved, as compared with the solutions known from the state of the art, by means of the reciprocal compensation of the frequency response of the septum polarizer and the further polarizer.